Reassessment of valve area determinations in mitral stenosis by the pressure half-time method: Impact of left ventricular stiffness and peak diastolic pressure difference

AbstractEstimation of the orifice area is of major importance in the timing of valve dilation or surgery in patients with mitral stenosis. Determination of the area has traditionally been accomplished at cardiac catheterization by the Gorlin equation. The valve area can also be estimated noninvasively with Doppler echocardiographic measurements of the pressure half-time, which is inversely proportional to the area. This method has gained widespread acceptance, but its accuracy has recently been questioned and factors other than reduction of orifice area appear to modify the pressure half-time. In the present study, the influence of left ventricular stiffness (defined as diastolic pressure rise per milliliter of mitral flow) and peak atrioventricular pressure difference on the pressure half-time was examined both in a hydraulic model and by review of data from 35 patients with mitral stenosis. Left ventricular stiffness <0.13 mm Hg/ml was considered normal.In the model study, the orifice area correlated only moderately with inverted pressure half-time (1/PHT) (r = 0.67). By multiple linear regression, inverted pressure half-time was shown to be dependent on valve area, chamber stiffness and peak pressure difference (R = 0.89), area and stiffness being most important (R = 0.85). In the clinical study, an increased ventricular stiffness was found in 22 of the 35 patients. The pressure half-time method overestimated the Gorlin-derived area by an average of 72% in these patients compared with only 10% in 13 patients with normal stiffness (p < 0.001). The overestimation was >100% in seven patients with coronary heart disease or aortic valve disease (or both), of whom all had a stiffness >0.2 mm Hg/ml.In conclusion, the pressure half-time is shortened and the valve area thus overestimated if left ventricular stiffness is increased, which is often the case in patients with mitral stenosis associated with coronary heart disease or aortic valve disease

Thermo gravimetric study of calcination of dolomite at pressurised conditions

Calcination and carbonation behaviour of dolomite has been studied in a pressurised thermo balance at pressures in the range of 1.1 to 2.3 MPa and for temperatures ranging from 730 to 840 degrees C. The atmosphere consisted of nitrogen containing up to 20 vol.-% carbon dioxide. The calcination of dolomite has been studied as a function of temperature, particle size, and P-CO2. An investigation concerning possible mass transfer restrictions for the experimental system and a model investigation of the calcination rate in CO2 atmosphere has been made. Further, the effect of calcination on the BET surface and the BET surface including the surface structure due to successive temperature cycles has been studied. The temperature for the initialisation of calcination of dolomite in CO2 atmosphere was independent of both P-CO2 and the particle size. No conclusive indications on mass transfer restrictions have been detected for the experimental system. A significant difference in calcination rate as a function of particle size existed for decomposition in CO2 atmosphere. A model for homogeneously progressing chemical reaction parallel with a shrinking core chemical reaction together with a mass transfer control mechanism was found to describe the calcination rate in CO2 atmosphere most accurately

On the intrinsic high temperature calcium oxide-sulfur dioxide reaction using the vacuum thermogravimetric analysis technique

The high temperature CaO/SO2 reaction was studied using four Swedish limestones and one dolomite as sorbents. The measurements were carried out in a vacuum thermogravimetric analysis (TGA) apparatus in order to investigate the intrinsic reaction mechanism. The reaction was found to be fast at the beginning due to the surface reaction, while the subsequent stage was controlled by the product layer diffusion, showing a lower reaction rate. The reaction rate increased as temperature increased up to 1000 degrees C in the range tested. SO2 partial pressure weakly affected the reaction. The fine sorbent particles used in the study resulted in the high CaO conversion. Further grinding of the sorbents gave a small increase in CaO conversion. Sintering generally decreased the initial reactivity but might not affect the ultimate CaO capacity. The larger pores in nascent CaO particles were valuable for the initial reaction conversion